Rabah Laouar

Stable isotope study of the igneous, metamorphic and mineralized rocks of the Edough complex, Annaba, Northeast Algeria

The petrogenesis of igneous, metamorphic and mineralized rocks in the Edough massif, NE Algeria, indicates an interplay between crustal and magmatic sources, and magmatic and surface fluids, as determined by sulphur and oxygen isotopic analyses. The Tertiary igneous rocks (microgranites and rhyolites) show a tendency towards I-type granitoids with δ34S values of +5.4±2.2‰ (1σ) and δ18O between +5.6‰ and +6.9‰, with the most hydrothermally altered rocks having the lowest δ18O values. This is indicative of seawater being a major component of the hydrothermal fluids. Seawater interaction with the granitoids produced enrichment in 34S of sulphide-sulphur in both the microgranites and associated skarn mineralization. However, in the Beleleita W–Sn–(Au) deposit, magmatic fluids dominated the mineralization, reflected by δ34S values of +1.7‰ and +1.8‰. The basement amphibolites of Kef Lakhal indicate derivation from a basaltic magma with δ18O ranging from +4.9‰ to +8.6‰. Locally altered amphibolite has the lowest δ18O values suggestive of meteoric water interaction, whereas the highest δ18O indicate the incorporation of crustal material during the genesis of the amphibolites. Crustal contamination is also reflected in their δ34S of −18‰ to +2.1‰, with the most contaminated rocks having the lowest δ34S. Host Palaeozoic mica schists with δ18O of +12.7‰ and δ34S of −13.2‰ and associated marbles (δ34S −9.9‰ to −17.4‰) are thought to be the most likely contaminants. At the Ain Barbar Fe–Cu–Pb–Zn deposit, δ34S values range between −9.6‰ and −10.8‰, indicating that the sulphide-sulphur and base-metals were likely leached from the host Cretaceous flysch and/or the underlying mica schists, with local Tertiary magmatic rocks providing the heat for local convection cells. At Boumaiza Fe-deposit, δ34S values of the sulphide-sulphur extend from −1.2‰ to −8.1‰ indicative of magmatic sulphur with the incorporation of substantial amounts of sulphur derived from the host mica schists.

The oceanic anoxic event 2 at Es Souabaa (Tebessa, NE Algeria): bio-events and stable isotope study

At the southern margin of the Tethys, the Es Souabaa area recorded traces of Oceanic Anoxic Event 2 (OAE2) around the Cenomanian-Turonian boundary (C/Tb). The dark, laminated, filament- and pyrite-bearing limestones represent the typical facies of this event. In terms of sedimentary environment, these features reflect a transgressive drowning that had induced hypoxia in these sedimentary environments. Such conditions favored the deposition and preservation of organic matter of marine origin, the distribution of which was controlled by paleogeography and halokinetic tectonics at that period. The OAE2 reached a climax between the last upper Cenomanian occurrence of Rotalipora cushmani and the lower Turonian occurrence of Whiteinella praehelvetica. Positive shift of the δ13C excursion along with relatively high total organic carbon (TOC) contents during OAE2 both indicate palaeo-environmental modifications enhanced by a significant change in primary marine productivity. Meanwhile, negative δ18O peaks in carbonates reflect increasing temperatures. Comparison of the data from this study with those from the neighboring Kalaat Senan section (Tunisia) suggests close similarities of events, although OAE2 is much more enhanced in Algeria.Située sur la marge méridionale de la Téthys, la zone d’Es Souabaa porte les traces de l’évènement anoxique océanique 2 (EAO 2) au passage Cénomanien-Turonien. Les calcaires sombres, laminés, en plaquettes et à filaments, accompagnés de pyrite, constituent le faciès type de cet évènement. En termes de milieux de dépôt, ce faciès est l’expression d’un approfondissement du milieu lié à une transgression induisant une sous-oxygénation du milieu. Ces conditions ont favorisé le dépôt et la conservation de matière organique d’origine essentiellement marine; sa distribution dépend essentiellement de la paléogéographie et de la tectonique halocinétique dans la région. L’EAO 2 y est à son paroxysme entre la dernière occurrence de Rotalipora cushmani au Cénomanien supérieur et l’apparition des Whiteinella praehelvetica au Turonien inférieur. L’excursion positive du δ13C, ainsi que les teneurs élevées en carbone organique total (COT), au cours de l’EAO 2 indiquent des modifications paléo-environnementales exacerbées par une productivité primaire marine importante. L’excursion négative du δ18O des carbonates traduit, quant à elle, une augmentation des paléo-températures. La comparaison des données d’Es Souabaa avec celles connues à Kalaat Senan (en Tunisie), montre d’étroites similitudes avec une exacerbation de l’EAO 2 du côté algérien.

The Oued Amizour VHMS Zn-Deposit, Northeastern Algeria: Does It Have a Kuroko-Type Signature?

The Oued Amizour granitoids (Fig. 1) were studied in order to assess the role of magma processes in the formation of the largest Zn-deposit in the region. The igneous rocks that host the giant Zn deposit, consist of two distinct lithologies: volcanic masses and subvolcanic-plutonic rocks, both of which suffered severe hydrothermal alterations. The boundary between the two lithologies is marked by a massive, ≈10 m thick anhydrite layer. Field observations and petrological study carried out at approximately 800 m length bore-hole that cross-cut the whole igneous masses show the following formations from the top to the bottom: pyroclastic rocks, andesites, porphyritic pyroclastic rocks, vesicular andesites, microgranites, tuff and lava flows, volcanic breccias and highly altered andesites that are intruded by aplites, metasomatized granodiorites and, finally, massive granodiorites. Open image in new window Fig. 1 a Geological sketch map of Bejaia-Oued Amizour region. b Simplified geological map of the Oued Amizour region showing the Ait Bouzid sector (After O.R.G.M 1998, unpub. doc.)